"A senior OpenBSD developer has complained on a mailing list that upstream vendors of free and open source software are adding in changes without any thought of whether downstream users could adapt to the change. Marc Espie said this would hurt smaller players by not allowing them to keep up with the changes. Basically what is happening is that numerous changes are being made to Linux and smaller projects like OpenBSD cannot keep up with the changes. And, according to Espie, not all these changes are strictly necessary."

There is a lot of talk about licenses and the old war between GPL and BSD going on here, but not a lot of talk about practical reasons or thoughts on what is going on upstream.
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I seriously don't see why anyone would ignore the obvious benefits of working with the BSD communities to improve their code.

Because the BSD licence can't guarantee the improvements will be passed back, whereas GPL obligates it (upon distribution). I'm not saying BSD don't pass back improvements, because they obviously do, but there's no guarantee.

It is a practical matter what licences to choose, and the guy who made the mailing list post did list licences as one of the major issues.